The present invention relates to an apparatus for the rapid recognition of short circuits and for generating an electrical trigger command with an electronic measuring and processing configuration for current values, which in a digital comparison circuit compared to predetermined limit values transmits the trigger command.
In a known configuration of the above mentioned kind (DE-OS No. 26 09 654) only the current is detected, so that no information about converted power, power factor and other parameters can be made and extraneous interferences also cannot readily be distinguished. The present invention is based on the task of creating a configuration of the above mentioned kind, in which, by avoiding the above mentioned drawbacks, the nature of the users in the operating state and their behavior can be ascertained. This is accomplished by the measuring configuration measuring the time variations of the current as well as the voltage of the grid and on that basis determining the complex impedances and power.
A configuration for influencing a switchgear as a function of data regarding the state of the grid through an impedance measuring device with a processing stage, which blocks switching on of the switchgear as a function of predetermined impedance values is known per se (DE-OS No. 33 47 209). The impedance measurements carried out here do not give direct information regarding the converted currents. In order to make determination of impedance values for individual associated discrete frequency values possible, so that some idea of the behavior of the impedance as a function of frequency can be obtained it is of advantage, if a configuration is provided, which converts the time variations of current and voltage into the associated frequency range. In order to extract the values characteristic for the impedance and classify them with respect to their magnitude from the general run of the impedance over the frequency it is advantageous if a configuration is provided, which carries out an identification calculation and completes classification of the electrical parameters of the installation component. In order to keep electronic interferences from reaching the evaluation it is advantageous, if a configuration for filtering the measured current and the voltage is provided before the subsequent investigations. Filtering measured values is known per se (8047 IEEE Trans. on Power Apparatus & Syst., Vol. PA8-99, 1980, Jan/Feb.. No 1, page 153). In order to build a reliable cost-efficient configuration of the above mentioned kind, it is advantageous if a configuration is provided, which converts the current and the voltage into digital number sequences after they are filtered and carries out the subsequent investigations with digital electric function modules. Digital to analog converters are also known from the above mentioned publication, page 153. In order to achieve shorter evaluation times it is advantageous if a configuration is provided which breaks down the digital number sequences into a time sequence of segments. In order to be able to compare the individual characterized parameters associated with the segments with each other, it is advantageous, if a configuration is provided, which separates the numerical sequences into a time sequence of segments with an equal number of measured values in each instance. In order to obtain an indication of reliability of the series connected measured value processor, it is advantageous if a configuration is provided, which for each segment carries out standardization to diminishing arithmetic means. Processing the measured values becomes simpler if a configuration is provided through which scaling can be carried out proportional to the measured values of the current and the voltage. If in a configuration the cross correlation function of the measured voltage and the current is formed, a measure for the similarity of the signals of the current and the voltage follows from this. If a configuration is provided, which utilizes the maximum for the cross correlation function as well as its position in time for the classification of the state of the installation, the time positions indicate quantifiable parameters for the state of the installation, while the cross correlation function represents a general measure of it. A simple method for converting signals into the frequency range results if a configuration is provided, which forms the Fourier transforms of the measured voltage and current. The conjugate-complex product of the Fourier transforms of the voltage and the current is a measure of the complex power converted in the installation. The determination of the amount and phase of individual frequency ranges of the product can be utilized for classifying the state of the installation. The amount and phase form a quantifiable value for the power converted in the installation with respect to the value and phase position of individual lines. For classifying the state of the installation, it is moreover of advantage if a configuration is provided in which the complex quotient of the Fourier transforms of voltage and current for the associated as well as the amount and the phase of individual frequency ranges of the quotient are formed. In order to avoid erroneous switching off through extraneous interferences it is of advantage if a configuration is provided, which depending on the grid, permits the preset parameters and limit values to automatically track the superposed high-frequency interference voltage and currents of the installation component. A simple adaptation to varying states of the grid, for example through switching-on of additional users, can take place, if a configuration is provided, which as a function of the variations of the grid state automatically tracks the pre-set parameters and limit values. In order to keep the evaluation time as short as possible, it is of advantage if several digital function modules are provided for parallel investigation of the measured currents and voltages. Further shortening of the evaluation time is accomplished, if the individual segments overlap in time and are simultaneously investigated parallel. An early simple short-circuit recognition can be achieved, if a configuration is provided which evaluates the time sequence of the parameters characterizing the individual segments. Here, for example, extrapolation is considered based on varying differences.